This section provides background information related to the present disclosure which is not necessarily prior art.
There is a strong interest in stretchable electrically conductive materials for use in a variety of diverse technological areas. Advanced implants and stretchable electronics require highly conductive materials that are elastic. For example, flexible electronics, neuroprosthetic and cardiostimulating implants, responsive curvilinear systems, advanced skins for robotics, and a variety of other applications require materials with increasingly high conductivity over increasingly large strains. However, while materials combining high stretchability and electrical conductivity are highly desirable, they are difficult to realize in practice. Molecular mechanisms of deformations and stiffening make combining high stretchability and conductivity fundamentally difficult.
Macroscale stretching of solids causes elongation and bending of chemical bonds. Such deformations lead to reduced overlap and delocalization of electronic orbitals, as well as degeneration of conduction pathways required for electronic conduction. Thus, macroscale stretching of solid materials causes elongation and bending of chemical bonds that are needed for electrical conduction (due to the transport of electrons along orbitals), causing a reduction in electrical conductivity. As such, even for purposefully designed stretchable conductors, electrical conductivity in materials decreases precipitously at tensile strains ranging from 130-150%. Aside from deformable solids, the dilemma between conductivity and stretchability can also be exemplified in liquid metals. Liquid metals have high electrical conductivities and can flow, but cannot be stretched because they are held by weak interatomic bonds. Thus, for these materials, efficient electron transport pathways are retained upon large deformation of shape, but liquid metals cannot be stretched because interatomic bonds are not strong enough.
Best known stretchable conductors partially overcome these problems by using percolated networks of high aspect ratio nanotubes or nanowires. Such materials typically have electrical conductivity of about 10 Scm−1 (or S/cm) and a maximum tensile strength (εmax) of 100%. However, these materials suffer from issues such as relatively low electrical conductivity and/or loss of elasticity that occurs with high carbon nanotube loading. Advanced and performance-hungry devices, such as neuroprosthetic implants or stretchable displays, require materials having conductivities 10,000 times higher, e.g., approaching the conductivities in metals (105 Scm−1), while retaining strains over 100%. Hence, realization of such devices thus far has been impeded by the lack of materials having the desired performance levels, which is in part due to the stretchability-conductivity dilemma. Accordingly, it would be desirable to develop highly stretchable electrically conductive materials that retain relatively high electrical conductivity even at high tensile strain levels. It would also be desirable to develop plasmonic materials based on stretchable materials having electric conductivity to provide plasmonic optical properties.